The invention relates generally to vacuum cleaners, and more particularly to a monitor for sensing the condition of a filter associated with a vacuum cleaner.
Vacuum cleaners are used to pick up a wide variety of items from a surface. The vacuum cleaners work by creating an air flow across the surface, causing dirt particles to be entrained in the air flow. The air flow may then be drawn past or through a filtering device to remove such entrained particles from the air stream. The air stream may then be vented.
Inducing the air flow is typically accomplished through the use of a motor driving a fan or impeller. Other well known means of generating the air flow are known in the industry, and are accordingly not described in greater detail here. The amount of energy necessary to generate the air flow is dependant on the amount of air required, as well as flow losses associated with the flow of the air stream across a surface being vacuumed, and across the filter. The amount of air required is a function of the cross sectional area of the air inlet adjacent to the surface being vacuumed, as well as the required velocity of the air across the surface being vacuumed. The higher the air velocity, the more likely that dirt will become entrained within the air stream, and thus be picked up from the surface.
A significant impact on the flow of the air stream, however, is the efficiency with which the air can pass through any filter media in the air stream. The impact on flow tends to be inversely proportional with the effectiveness of the filter in removing entrained particles from the air stream, i.e., the more effective the filter is at removing particles, the greater the flow loss that must be overcome by the device inducing the air flow. Furthermore, the flow loss across the filter may increase as the filter becomes clogged with particles that have been removed from the air stream.
As the flow loss caused by the filter increases, such as when the filter becomes full of collected particles or material, the motion of the air stream is impeded, typically such that the air stream comprises a smaller volume of air for a given period of time. Additionally, a greater pressure drop will occur across the filter as the filter creates a greater impedance to the flow of air.
As the impedance to flow increases, the amount of air being drawn through the air inlet by the flow inducing device decreases, the velocity of the air stream at the suction entrance of the vacuum cleaner decreases, decreasing the effectiveness of the vacuum cleaner. This decreased effectiveness may be wasteful of energy, to whit, that more time must be spent across a given area to successfully clean the area, as well as be frustrating for the operator of the vacuum cleaner. Accordingly, the ability to detect and signal such a reduced effectiveness to an operator is important
Prior art devices utilize a mechanical pressure gauge calibrated to indicate the increase in a pressure drop according to the condition of the filter. Such devices may show a range of the gauge indicator as being unsatisfactory, however the lack of a discrete indication leads to use of the vacuum cleaner in the inefficient, clogged filter condition, since the operator is not provided with a discrete signal that the filter must be cleaned or changed.
Accordingly, it is desirable to provide a filter sensor and monitor that effectively signals to a user that it is time to address the condition of the filter.